Influence of cultivation conditions on citrate production by Aspergillus niger in a semi-pilot-scale plant

The influence of some fermentation parameters on the semi-pilot scale (alteration of growth conditions, e.g., sugar concentration, incubation temperature and initial pH) on citrate production was demonstrated in parent and mutant strains of Aspergillus niger. Raw material from sugar industry (cane molasses) was examined as basal fermentation medium in a stirred stainless-steel 15-L fermentor. After growth on medium with 150 g/L sugar, the parent strain produced 51.2 g/L citric acid; the mutant strain achieved production maximum of 96.2 g/L. Comparing the growth, kinetic (volumetric substrate uptake rate, rate of substrate consumption and volumetric productivity rate) and production parameters it was found that the mutant strain grows more rapidly, with slightly changed morphology (intermediate, shiny round pellets with diameter 0.6-0.7 mm), and exhibits a higher citrate production and higher efficiency of sugar utilization.